Hydrogen-induced Sulfur Vacancies on the MoS2 Basal Plane Studied by Ambient Pressure XPS and DFT Calculations.

Sulfur vacancy on an MoS2 basal plane plays a crucial role in device performance and catalytic activity; thus, an understanding of the electronic states of sulfur vacancies is still an important issue. We investigate the electronic states on an MoS2 basal plane by ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and density functional theory calculations while heating the system in hydrogen. The AP-XPS results show a decrease in the intensity ratio of S 2p to Mo 3d, indicating that sulfur vacancies are formed. Furthermore, low-energy components are observed in Mo 3d and S 2p spectra. To understand the changes in the electronic states induced by sulfur vacancy formation at the atomic scale, we calculate the core-level binding energies for the model vacancy surfaces. The calculated shifts for Mo 3d and S 2p with the formation of sulfur vacancy are consistent with the experimentally observed binding energy shifts. Mulliken charge analysis indicates that this is caused by an increase in the electronic density associated with the Mo and S atoms around the sulfur vacancy as compared to the pristine surface. The present investigation provides a guideline for sulfur vacancy engineering.

Direct observation of the electronic states of photoexcited hematite with ultrafast 2p3d X-ray absorption spectroscopy and resonant inelastic X-ray scattering.

Hematite, α-Fe2O3, is an important semiconductor for photoelectrochemical water splitting. Its low charge carrier mobility and the presence of midgap states provide favourable conditions for electron-hole recombination, hence affecting the semiconductor's photoelectrochemical efficiency. The nature of the excited state and charge carrier transport in hematite is strongly debated. In order to further understand the fundamental properties of the hematite photoexcited state, we conducted femtosecond 2p (L3) X-ray absorption (XAS) and 2p3d resonant inelastic scattering (RIXS) measurements on hematite thin-films at the Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL). The observed spectral changes and kinetic processes are in agreement with previous 3p XAS reports. The potential additional information that could be acquired from 2p3d RIXS experiments is also discussed.

Reversible low-temperature redox activity and selective oxidation catalysis derived from the concerted activation of multiple metal species on Cr and Rh-incorporated ceria catalysts.

The ceria-based catalyst incorporated with Cr and a trace amount of Rh (Cr0.19Rh0.06CeOz) was prepared and the reversible redox performances and oxidation catalysis of CO and alcohol derivatives with O2 at low temperatures (<373 K) were investigated. In situ X-ray absorption fine structure (XAFS), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM)-EDS/EELS and temperature-programmed reduction/oxidation (TPR/TPO) revealed the structures and redox mechanisms of three metals in Cr0.19Rh0.06CeOz: dispersed Rh3+δ species (<1 nm) and Cr6-γO3-x nanoparticles (∼1 nm) supported on CeO2 in Cr0.19Rh0.06CeOz were transformed to Rh nanoclusters, Cr(OH)3 species and CeO2-x with two Ce3+-oxide layers at the surface in a concerted activation manner of the three metal species with H2.

Strong Hydrogen Bonds at the Interface between Proton-Donating and -Accepting Self-Assembled Monolayers on Au(111).

Hydrogen-bonding heterogeneous bilayers on substrates have been studied as a base for new functions of molecular adlayers by means of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRAS), and density functional theory (DFT) calculations. Here, we report the formation of the catechol-fused bis(methylthio)tetrathiafulvalene (H2Cat-BMT-TTF) adlayer hydrogen bonding with an imidazole-terminated alkanethiolate self-assembled monolayer (Im-SAM) on Au(111). The heterogeneous bilayer is realized by sequential two-step immersions in solutions for the individual Im-SAM and H2Cat-BMT-TTF adlayer formations. In the measurements by AFM, a grained H2Cat-BMT-TTF adlayer on Im-SAM is revealed. The coverage and the chemical states of H2Cat-BMT-TTF on Im-SAM are specified by XPS. On the vibrational spectrum measured by IRAS, the strong hydrogen bonds between H2Cat-BMT-TTF and Im-SAM are characterized by the remarkably red-shifted OH stretching mode at 3140 cm-1, which is much lower than that for hydrogen-bonding water (typically ∼3300 cm-1). The OH stretching mode frequency and the adsorption strength for the H2Cat-BMT-TTF molecule hydrogen bonding with imidazole groups are quantitatively examined on the basis of DFT calculations.

Enhancement of CO2 adsorption on oxygen-functionalized epitaxial graphene surface under near-ambient conditions.

The functionalization of graphene is important in practical applications of graphene, such as in catalysts. However, the experimental study of the interactions of adsorbed molecules with functionalized graphene is difficult under ambient conditions at which catalysts are operated. Here, the adsorption of CO2 on an oxygen-functionalized epitaxial graphene surface was studied under near-ambient conditions using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). The oxygen-functionalization of graphene is achieved in situ by the photo-induced dissociation of CO2 with X-rays on graphene in a CO2 gas atmosphere. The oxygen species on the graphene surface is identified as the epoxy group by XPS binding energies and thermal stability. Under near-ambient conditions of 1.6 mbar CO2 gas pressure and 175 K sample temperature, CO2 molecules are not adsorbed on the pristine graphene, but are adsorbed on the oxygen-functionalized graphene surface. The increase in the adsorption energy of CO2 on the oxygen-functionalized graphene surface is supported by first-principles calculations with the van der Waals density functional (vdW-DF) method. The adsorption of CO2 on the oxygen-functionalized graphene surface is enhanced by both the electrostatic interactions between the CO2 and the epoxy group and the vdW interactions between the CO2 and graphene. The detailed understanding of the interaction between CO2 and the oxygen-functionalized graphene surface obtained in this study may assist in developing guidelines for designing novel graphene-based catalysts.

New soft X-ray beamline BL07LSU at SPring-8.

A new soft X-ray beamline, BL07LSU, has been constructed at SPring-8 to perform advanced soft X-ray spectroscopy for materials science. The beamline is designed to achieve high energy resolution (E/ΔE> 10000) and high photon flux [>10(12) photons s(-1) (0.01% bandwidth)(-1)] in the photon energy range 250-2000 eV with controllable polarization. To realise this state-of-the-art performance, a novel segmented cross undulator was developed and adopted as a light source. The details of the undulator light source and beamline monochromator design are described. The achieved performance of the beamline, such as the photon flux, energy resolution and the state of polarization, is reported.

Science electives in high school will improve nutrition knowledge but not enough to make accurate decisions.

BACKGROUND/OBJECTIVES: Nutrition knowledge has been reported to have a weak positive effect on healthy eating behavior. This study aimed to determine if there was a difference in nutrition knowledge depending on the choice of science subject in high school and whether that affected the actual eating habits of college students in Japan. SUBJECTS/METHODS: The subjects were 514 college students, the majority first-year students, in 3 cities in Japan. A questionnaire survey was conducted on elective subjects in science in high school, diet (11 items), lifestyle (5 items), and nutrition knowledge (34 questions). The preliminary survey was conducted on 47 students in the fall of 2019, and the full-scale survey was conducted in May-June and October-November 2021 at the end of lectures for the first-year students. RESULTS: The students in the high-score group (24-31 points, n = 180) had a higher intake of vegetables (odds ratio [OR], 1.78; 95% confidence interval [CI], 1.12-2.82; P = 0.015) and breakfast (OR, 1.64; 95% CI, 1.03-2.60; P = 0.035), and a reduced intake of fast food (OR, 0.27; 95% CI, 0.14-0.51; P < 0.001) than those in the low-score group (6-19 points, n = 150). Only the biology and chemistry students had significantly higher nutrition scores than the other groups (all: P < 0.001), but no significant difference was found between the other groups. Understanding nutrition learned in elementary and junior high school is appropriate, while molecular structure, recommended amount, and food poisoning were insufficient. CONCLUSIONS: Knowledge of nutrition appears to have a positive effect on the actual eating habits of college students. Although biology and chemistry in high school may help students understand the foundations of good nutrition, specialized food education may be required to make informed dietary choices.

Surface Exchange Reaction of Mixed Conductive La0.65Ca0.35FeO3-δ during Oxygen Evolution and Incorporation as Traced by Operando X-ray Photoelectron Spectroscopy.

High oxygen permeability of mixed conductive La0.65Ca0.35FeO3-δ (LCF) is applicable to pure oxygen gas generators and cathodes for solid oxide fuel cells, etc.; however, lower surface exchange reactions at temperatures below 800 °C reduce permeability. To understand the microscopic surface reaction mechanism, operando soft X-ray photoelectron spectroscopy of an LCF film surface was conducted during the evolution and incorporation of oxygen. LCF film was prepared on yttria-stabilized zirconia and a current was applied throughout the film at ∼600 °C. From operando X-ray photoelectron spectra, surface oxide species involved in the surface exchange reaction obviously appeared on the film during the evolution of oxygen from the surface. The number of surface oxide species abruptly decreased during incorporation of oxygen. By applying the current from a negative to positive value, the numbers of surface oxide species and ligand holes near Fe3+ ions on the surface both significantly increased. The results infer that ligand holes in the Fe 3d-O 2p hybrid orbitals correspond to active reaction sites at which surface oxide species change to oxygen molecules. Increasing the number of active reaction sites is key to improving oxygen evolution of mixed conductive oxides.

Hole Dynamics in Photoexcited Hematite Studied with Femtosecond Oxygen K-edge X-ray Absorption Spectroscopy.

Hematite (α-Fe2O3) is a photoelectrode for the water splitting process because of its relatively narrow bandgap and abundance in the earth's crust. In this study, the photoexcited state of a hematite thin film was investigated with femtosecond oxygen K-edge X-ray absorption spectroscopy (XAS) at the PAL-XFEL in order to follow the dynamics of its photoexcited states. The 200 fs decay time of the hole state in the valence band was observed via its corresponding XAS feature.

Femtosecond Charge Density Modulations in Photoexcited CuWO4.

Copper tungstate (CuWO4) is an important semiconductor with a sophisticated and debatable electronic structure that has a direct impact on its chemistry. Using the PAL-XFEL source, we study the electronic dynamics of photoexcited CuWO4. The Cu L3 X-ray absorption spectrum shifts to lower energy upon photoexcitation, which implies that the photoexcitation process from the oxygen valence band to the tungsten conduction band effectively increases the charge density on the Cu atoms. The decay time of this spectral change is 400 fs indicating that the increased charge density exists only for a very short time and relaxes electronically. The initial increased charge density gives rise to a structural change on a time scale longer than 200 ps.

Structural inhomogeneity of interfacial water at lipid monolayers revealed by surface-specific vibrational pump-probe spectroscopy.

We report vibrational lifetime measurements of the OH stretch vibration of interfacial water in contact with lipid monolayers, using time-resolved vibrational sum frequency (VSF) spectroscopy. The dynamics of water in contact with four different lipids are reported and are characterized by vibrational relaxation rates measured at 3200, 3300, 3400, and 3500 cm(-1). We observe that the water molecules with an OH frequency ranging from 3300 to 3500 cm(-1) all show vibrational relaxation with a time constant of T(1) = 180 ± 35 fs, similar to what is found for bulk water. Water molecules with OH groups near 3200 cm(-1) show distinctly faster relaxation dynamics, with T(1) < 80 fs. We successfully model the data by describing the interfacial water containing two distinct subensembles in which spectral diffusion is, respectively, rapid (3300-3500 cm(-1)) and absent (3200 cm(-1)). We discuss the potential biological implications of the presence of the strongly hydrogen-bonded, rapidly relaxing water molecules at 3200 cm(-1) that are decoupled from the bulk water system.

Ultrafast inter- and intramolecular vibrational energy transfer between molecules at interfaces studied by time- and polarization-resolved SFG spectroscopy.

We present experimental results on femtosecond time-resolved surface vibrational spectroscopy aimed at elucidating the sub-picosecond reorientational dynamics of surface molecules. The approach, which relies on polarization- and time-resolved surface sum frequency generation (SFG), provides a general means to monitor interfacial reorientational dynamics through vibrations inherent in surface molecules in their electronic ground state. The technique requires an anisotropic vibrational excitation of surface molecules using orthogonally polarized infrared excitation light. The decay of the resulting anisotropy is followed in real-time. We employ the technique to reveal the reorientational dynamics of vibrational transition dipoles of long-chain primary alcohols on the water surface, and of water molecules at the water-air interface. The results demonstrate that, in addition to reorientational motion of specific molecules or molecular groups at the interface, inter- and intramolecular energy transfer processes can serve to scramble the initial anisotropy very efficiently. In the two exemplary cases demonstrated here, energy transfer occurs much faster than reorientational motion of interfacial molecules. This has important implications for the interpretation of static SFG spectra. Finally, we suggest experimental schemes and strategies to decouple effects resulting from energy transfer from those associated with surface molecular motion.

Autocatalytic water dissociation on Cu(110) at near ambient conditions.

Autocatalytic dissociation of water on the Cu(110) metal surface is demonstrated on the basis of X-ray photoelectron spectroscopy studies carried out in situ under near ambient conditions of water vapor pressure (1 Torr) and temperature (275-520 K). The autocatalytic reaction is explained as the result of the strong hydrogen-bond in the H2O-OH complex of the dissociated final state, which lowers the water dissociation barrier according to the Brønsted-Evans-Polanyi relations. A simple chemical bonding picture is presented which predicts autocatalytic water dissociation to be a general phenomenon on metal surfaces.

Discovery of long-acting N-(cyanomethyl)-N-alkyl-L-prolinamide inhibitors of dipeptidyl peptidase IV.

Details of structure-activity relationships (SAR) for P2 moiety of a P1 2-cyanopyrrolidine dipeptidyl peptidase IV (DPP-IV) inhibitor 4a including stereochemistry are presented. Based on this information, a series of P1 (N-alkyl)aminoacetonitrile analogs 9-20 possessing optimal P2 structure were synthesized and evaluated as inhibitors of DPP-IV. Among them, a representative compound 11, N-(cyanomethyl)-N-ethyl-L-prolinamide, was further evaluated to determine its effect on the plasma glucose level. Also 4a, 10, and 11 were evaluated for their isozyme selectivity to predict their safety problems.

Design and synthesis of DPP-IV inhibitors lacking the electrophilic nitrile group.

A series of (4beta-substituted)-L-prolylpyrrolidine analogs lacking the electrophilic nitrile function were synthesized and their dipeptidyl peptidase IV (DPP-IV) inhibitory activity and duration of ex vivo activity were evaluated. Structural optimization of a N-(3-phenyl-1,2,4-thiadiazol-5-yl)piperazine analog 8, which was found by high-speed analog synthesis, was carried out to improve the potency and duration of action. A representative compound 26 was evaluated to assess its effect on the plasma glucose level after the oGTT (oral glucose tolerance test) in normal rats. Structure-activity relationships (SAR) are also presented.

Water adsorption on Rh(111) at 20 K: from monomer to bulk amorphous ice.

The adsorption of water (D(2)O) molecules on Rh(111) at 20 K was investigated using infrared reflection absorption spectroscopy (IRAS). At the initial stage of adsorption, water molecules exist as monomers on Rh(111). With increasing water coverage, monomers aggregate into dimers, larger clusters (n = 3-6), and two-dimensional (2D) islands. Further exposure of water molecules leads to the formation of three-dimensional (3D) water islands and finally to a bulk amorphous ice layer. Upon heating, the monomer and dimer species thermally migrate on the surface and aggregate to form larger clusters and 2D islands. Based on the temperature dependence of OD stretching peaks, we succeeded in distinguishing water molecules inside 2D islands from those at the edge of 2D islands. From the comparison with the previous vibrational spectra of water clusters on other metal surfaces, we conclude that the number of water molecules at the edge of 2D islands is comparable with that of water molecules inside 2D islands on the Rh(111) surface at 20 K. This indicates that the surface migration of water molecules on Rh(111) is hindered as compared with the cases on Pt(111) and Ni(111) and thus the size of 2D islands on Rh(111) is relatively small.

Parameter determination procedure for extended Hückel approximation and its application for solid-state electrolytes.

A determination procedure of transferable tight-binding parameters of extended Hückel approximation with charge self-consistency is explained, which is applicable to both molecules and crystalline solids. The parameters are adjusted by optimizing evaluation functions, compared with reference results of energy levels or band structure calculated by, for example, the density functional theory. By introducing the evaluation function, the automatic optimization of the parameters for small molecules and clusters is achieved, which makes it easy to determine an accurate parameter set and a wide application of the TB scheme. A practical procedure of parameter optimization is demonstrated for solid-state electrolytes of Li4GeS4 and Li3PS4.

Surgical management of retinal detachment associated with myopic macular hole: anatomic and functional status of the macula.

PURPOSE: To evaluate the postoperative status of the macula after vitreous surgery with internal limiting membrane removal for macular hole related retinal detachment in patients with severe myopia. DESIGN: Interventional case series. METHODS: We prospectively examined 10 eyes with retinal detachment associated with a myopic macular hole from 10 consecutive patients, and performed pars plana vitrectomy with internal limiting membrane peeling. Macular buckling was performed in one eye during the initial treatment and in three eyes during subsequent operations. The main outcome measures were the anatomic reattachment rate and the postoperative status of the macular hole. We examined the macular area pre- and postoperatively with slit-lamp biomicroscopy and with a scanning laser ophthalmoscope. Cross-sectional imaging of the macular area was conducted with optical coherence tomography. RESULTS: Successful retinal reattachment was achieved in seven eyes (70%) after the initial surgery and in three eyes (30%) after additional procedures. Visual acuity remained unchanged in two eyes (20%), and improved by two or more logarithmic units of minimum angle of resolution (logMAR) measurement in eight eyes (80%). The macular hole was anatomically closed in only one eye (10%). Postoperative enlargement of the macular hole was observed in seven eyes. CONCLUSIONS: In highly myopic eyes with macular hole related retinal detachment, closure of the macular hole is difficult to attain despite the complete relief of tangential traction by internal limiting membrane peeling. Results indicate the presence of a possible imbalance between the retina and the choroid-sclera complex associated with axial elongation and posterior staphyloma in highly myopic eyes.

Orally active PDE4 inhibitor with therapeutic potential.

Based on the promising results obtained by the clinical trial of Ariflo, further optimization of the spatial arrangement of the three pharmacophores (the carboxylic acid moiety, nitrile moiety and 3-cyclopentyloxy-4-methoxyphenyl moiety) in the structure of Ariflo 1 was attempted using a bicyclo[3 ?3 ?0]octane template with more stereochemical diversity than the cyclohexane template of Ariflo 1. Biological evaluation of the decyanated analogs and further optimization of the cyclopentyloxy moiety of 2a-b were also performed. Among the compounds tested, 2a, 7a-b and 12a were found to be orally active and were estimated to have therapeutic potential based on cross-species and same-species comparisons. The structure-activity relationships (SARs) of these compounds were investigated and pharmacokinetic data for 2a and 7b were also obtained by single-dose studies in rats.

Observation of human corneal and scleral collagen fibrils by atomic force microscopy.

PURPOSE: We attempted to analyze the three-dimensional ultrastructure of human corneal and scleral collagen fibrils with an atomic force microscope (AFM). METHODS: A normal eye removed from a 66-year-old male patient during therapy was used in this study. Suspended corneal and scleral collagen fibrils were individually attached to glass slides by centrifugation. These collagen fibrils were air-dried and observed with a noncontact-mode AFM in air. RESULTS: AFM imaging provided information on the surface topography of both corneal and scleral collagen fibrils. The corneal collagen fibrils had a height of 11.9 +/- 1.0 nm (mean +/- SD) and scleral fibrils a height of 82.5 +/- 35.6 nm. A periodic banding pattern of grooves and ridges was clearly found on both types of fibrils; the D-periodicity and the groove depth were 65.7 +/- 0.8 nm and 1.46 +/- 0.50 nm in the corneal fibrils, and 67.3 +/- 1.1 nm and 6.16 +/- 1.23 nm in the scleral fibrils. CONCLUSIONS: Surface topographic images of human corneal and scleral collagen fibrils were clearly obtained with the AFM. This technique provides quantitative information on the surface morphology of the collagen fibrils at high resolution.